What are some common methods for a PHP server to automatically notify a client, such as in a messaging system?

One common method for a PHP server to automatically notify a client in a messaging system is to use WebSockets. WebSockets allow for real-time communication between the server and client, enabling instant notifications. Another approach is to use AJAX polling, where the client periodically sends requests to the server to check for new messages. Lastly, server-sent events (SSE) can be utilized to push notifications from the server to the client without the need for continuous polling.

// Example using WebSockets
// Server-side code
$server = new swoole_websocket_server("0.0.0.0", 9501);

$server->on('open', function (swoole_websocket_server $server, $request) {
    echo "New client connected: {$request->fd}\n";
});

$server->on('message', function (swoole_websocket_server $server, $frame) {
    echo "Received message: {$frame->data}\n";
    $server->push($frame->fd, "Server: Message received");
});

$server->start();